Bosch's sintered filter cuts particulates

The filter can be regenerated 20 to 30 percent faster than comparable ceramic filters because of its construction, said Ulrich Dole, president of Bosch's diesel systems division, at a briefing here.

"The filter is made out of sintered metal and can handle a higher ash loading than traditional silicon-carbide filters, making it suitable for high-vehicle mileages," Dole said.

Sintering is a process used to heat powdered metals, causing them to bond together in a matrix. The matrix can be made more or less porous as needed.

Sintered bronze is used for bearings, for example, because its porosity can hold lubricants.

A sintered diesel filter traps soot particles and holds them pending "regeneration." At that time, the trap is heated to about 2,500 degrees Fahrenheit with a dose of fuel and air that burns soot particles into water and carbon dioxide. Unlike ceramic matrix filters, the metal filters can better handle heating cycles.

Adding a high-efficiency particle filter lets diesels run at minimal NOx levels. "This target would make it necessary for all diesel cars to (have) particulate filters," Dole said.

Besides using high fuel pressure and numerous injections inside the combustion chamber to reduce diesel emissions, Bosch is considering further emissions treatment. Options include using storage catalysts that can trap nitrogen oxide and reduction catalysts that can break NOx down using a urea solution known as AdBlue.